Tuned microwave wattmeter



June 28, 1949. H. E. WEBBER TUNED MICROWAVE WATTMETER Original Filed Dec. 13, 1943 2 Sheets-Sheet 1 INVENTOR HU H E. WEBBER BY #bm ATTORNEY June 28, 1949. H. E. WEBBER Re- 23,131

TUNED MI CROWAVE WATTMETER Original Filed Dec. 13, 1943 2-Sheets-Sheet 2 MLM INVENTOR H GH :.wEBBER Bv m.

ATTORNEY Reissued June 28, 1949 TUNED MICROWAVE WATTMETER Hugh E. Webber, Huntington, N. Y., assignor to The Sperry Corporation, a corporation of Dela- Original No. 2,419,613, dated April 29, 1947, Serial No. 514,111, December 13, 1943.

Application for reissue April 29, 1947, Serial No. '750,841

12 Claims.

The present application is a continuation-inpart of my copending application Serial No. 53.3,- 164, led December 6, 1943.

The present invention relates to tuned microwave wattmeters.

An object of my invention is to provide methods and apparatus for measuring power at frequencies in the microwave region.

More particularly, it is an object oi my invention to provide a hollow pipe wave guide type of wattmeter.

Another object of my invention is to provide an improved arrangement for dissipating energy in a wave guide, for avoiding reflections from energy absorbing devices in the wave guide and for matching impedances in a wave guide.

It is an object to provide improved arrangements for coupling a power absorbing wire or lament to a wave guide.

Another object is to provide a microwave wattmeter having ambient temperature compensation.

Still another object of the invention is to provide wave guide apparatus which may be tuned by an adjustable probe.

A further object of the invention is to provide a mounting arrangement for a tuning probe with both axial and transverse adjustment.

Other and further objects and advantages of the invention will become apparent as the description proceeds.

In carrying out the invention in its preferred form. microwave energy, the power of which is to be measured, is conveyed through a hollow pipe wave guide type of transmission line and a power-absorbing hot wire such as a barretter wire is mounted athwart the wave guide.

Means are provided for matching the impedance of the barretter Wire to the line.

For ascertaining the radio frequency power consumed in the barretter wire, direct current is supplied to it, means are provided for measuring the direct current power input, and means are provided for measuring the resistance of the wire and maintaining it constant by adjusting the supply of direct current. Variations in the direct current power required to maintain constant resistance then represent variations in radio frequency power supplied to the wire by the transmission line.

A better understanding of the invention will be afforded by the following detailed description, considered in conjunction with the accompanying drawings, wherein:

Fig. 1 is a View of a barretter wire holder for a microwave wattmeter shown as cut by a longitudinal plane;

Fig. 2 is a fragmentary view in longitudinal section of a portion of the apparatus of Fig. 1 represented as cut by a plane 2-2 of Fig. 1;

Fig. 3 is a circuit diagram of a bridge circuit which may be employed in conjunction with the apparatus of Fig. 1 for maintaining the directcurrent (or low-frequency alternating-current) resistance of the variable wire and measuring the direct current power input thereto;

Fig, 4 is a longitudinal View of a barretter wire holder employing an adjustable probe for tuning;

Fig. 5 is a cross-sectional view of a portion of the apparatus of Fig. 4 cut by the plane 5--5 indicated in Fig. 4; and

Fig. 6 is a fragmentary longitudinal sectional View of a portion of the apparatus of Fig. 4 as cut by a plane G-B in Fig. 4.

Like reference characters are utilized throughout the drawings to designate like parts.

In my aforesaid parent application, I have described a high frequency wattmeter employing a bridge circuit for measuring the direct current resistance of a barretter wire to which both alternating and direct currents are supplied. A similar bridge circuit may be employed in connection with the measurement of power of ultrahigh-frequency energy conveyed through a hollow pipe wave guide type of transmission line. In my aforesaid application I have described suitable holders for barretter wires Where the alternating current energy Was conveyed through coaxial transmission lines. I also described suitable constructions for such barretter wires, particularly in connection with the measurement of low power, in which case a ne barretter wire was required.

In the present application wire holders are described for circuits in which radio frequency energy is supplied through wave guide transmission lines.

summarizing from my aforesaid application, the bridge, as illustrated in Fig. 3 of the present application, comprises four arms Il, l2, I3 and H, with a diagonal arm I5 and a current source I6. The arm I3 includes a resistor il and a current-responsive device such as a milliammeter IB in series. The arm I4 comprises a barretter wire unit including a fine wire or lament I9 which constitutes the actual resistance of the arm i4 of the bridge. For supporting the wire I9 and making direct-current and microwave alternating-current connections, the wire I9 and the unit I4 containing it are mounted in a Wire holder 2| represented schematically in Fig. 3 and sho-wn in greater detail in l or Fig. 4. The diagonal arm |5 includes a galvanometer 22 and a sensitivity-adjusting rheostat F53 connected in series between conjugate points 2li and 25 of the bridge.

The direct current source I6 is connected to the remaining pair of conjugate points 2E and 83 of the bridge in series with direct current power adjusting rheostats 23 and a switch 28.

The resistors and I2 may be standard resistors arranged to maintain substantially constant resistance, and the resistor |1 is so chosen as to have a resistance which, when added to the resistance of the milliammeter I3, will produce a totol resistance for the bridge arm |3 of a proper value to balance the bridge when the barretter wire I3 has a predetermined resistances corresponding to the maximum power input and temperature considered desirable for the barretter wire I9.

If ambient temperature compensation is desired, one of the resistors such as the bridge arm I2 will take the form of a compensating resistor mounted in proximity to the barretter wire unit |4 within the wire holder 2|.

The wire holder shown in Fig. 1 comprises a self-shielding type of transmission line such as a rectangular hollow pipe wave guide 3| open at the left-hand end and having a choke coupling 32 mounted thereon for connecting the open end of the line to an input line and corresponding choke coupling (not shown) The narrow dimension of the wave guide 3| is that shown in Fig. 1, and the wide dimension is that shown in Fig. 2. Suitable supporting means are provided for mounting the barretter wire unit I4 athwart the wave guide 3| parallel to the narrow dimension thereof.

For enabling a direct current connection to be made to the barretter wire unit |4 without interposing radio frequency impedance in the line 3| or causing reflections therein, a short transverse line or lateral tuning stub 33 is provided. In the arrangement shown, the tuning stub 33 is of the concentric, substantially circular transmission line type. For tuning the lines and matching the impedance of the line to that of the barretter I9, the wave guide 3| is provided with a line-length adjusting mechanism 34 closing the right-hand end of the line 3|, and the stub line 33 is provided with a corresponding adjusting mechanism 35.

The choke coupling 32 may be one of the type already known to those skilled in the art and illustrated and described in greater detail in the copending application of William A. Hayes, Serial No. 503,613, now abandoned, filed September 24, 1943. Briey, such a choke coupling comprises a circular block having a rectangular opening fitted over the line 3| and having wave trap slots 36 cut therein, the slots 36 being a quarter-wave deep and a quarter-wave distant from the edge of the line 3|.

The adjusting mechanism 34 closing the righthand end of the wave guide 3| comprises a quarter-wave trap 31 mounted within the guide 3| to form a short-circuiting plug which is adjustable in longitudinal position. The trap 31 comprises a hollow rectangular-shaped member with a base 38 slightly smaller than the internal dimensions of the Wave guide 3| and having longitudinally extending sides or web portions 39 one quarter wave in length which serve as a wave trap and assure substantially zero impedance closure of the wave guide transmisison line 3| substantially at the surface 38. For supporting the trap member 31, a positioning means is provided including a sliding block 4| having a slip t within the wave guide 3|, a supporting rod 42 staked into the base 38 of the trap member 31 and also inserted with adrive nt' into an opening in the sliding block 4I4 and adjusting means such as a micrometer screw arrangement. The micrometer screw arrangement includes a block 43 secured in the end of the wave guide 3| and having a threaded opening, a hollow screw 44 having a knurledhead 45, an internal screw 4G having a slotted head 41 and having a tapped opening 4B at the opposite end thereof, and a threaded extension 49 of the rod 42 fitting the tapped opening 43 of the internal screw 46. The screw head is counterbored to receive the screw head 41 with a loose t. Set screws 50 are provided to prevent the internal screw 46 from turning with respect to the screw 43 and the block 4|.

The stub line 33 includes an outer hollow cylinder 5| and an inner conductor rod 52. The linelength adjusting mechanism 35 closing the end of the line 33 includes an axially movable hollow cylindrical block 53 fitting the center rod 52 and of slightly smaller diameter than the internal surface of the cylinder 5|, having a toroidal or hollow cylindrical downward projection 54 carrying two wave trap members 55 secured and electrically connected to the member 54 at the lower end and extending upward with clearance so as to avoid contact with the internal rod 52, the outer cylinder 5|, the supporting projection 54, or a shoulder 56 of the slidable member 53. For slidably supporting the member 53 within the hollow cylinder 5|, ring-shaped shoe members 51 composed of suitable material such as brass are provided. For enabling the rod 52 to be supported at the upper end, it is formed with a head 58, and a cap 59 is provided which is adapted to clamp the head 58 against the top of the cylinder 5 For supporting' the intermediate or lower portion of the rod 52 according to the position of the member 53, a relatively close slide flt is made between the member 53 and the rod 52.

For fixing the axial position of the member 53 with respect to the cylinder 5|, the outer surface of the cylinder 5|` is threaded. A pair of pins 50 is inserted in the member 53 with a drive fit, and a slotted positioning nut 6| is provided. The positioning nut 8| comprises a cup-shaped member B2 with an annular block B3 fastened therein, for example, by a machine screw 64 and spaced suiiiciently from the base of the eupshaped member 52 to form a slot 65 for receiving the pins B0. The inner surface of either the cupshaped member 62 or the annular block 53 may be threaded to engage the outer surface of the hollow cylinder 5|. If desired, a ring shaped lock nut 65 may also be provided. The cylinder 5| is tted into the tcp surface of the wave guide 3| and mechanically and electrically connected thereto as by soldering or welding, a smooth internal joint being employed so as to maintain a flat internal surface for the wave guide 3|.

The lower end of the rod 52 is countersunk and may also be slotted at one side to form a retaining spring socket 61 for the upper end of the `barretter wire unit I4.

The unit I4, as shown, comprises an insulating tubular body 68 carrying a pair of ferrules 69 closing the ends of the tube 53 and electrically connected to the ends of the barretter wire I3. For supporting the lower end of the barretter unit |4, a second spring clip or socket 1| is provided, and for making direct current connections to the Wire I9, a direct current connector 12 is provided. The supporting means for the lower socket 1| and the connector 12 include a hollow block 13 of substantially circular crosssection, a cup-shaped fitting 14, an insulating shell 15, a lock nut 19, and insulating bushings 11 and 18.

For the purpose of avoiding the interposition of a discontinuity in the microwave transmission line 3|, a wave trap in the form of a shouldered hollow cylinder 19 is provided. The block 13 is fitted into the lower surface of the wave guide 3| and mechanically and electrically connected thereto, and the member 19 is fitted into the top end of the member 13 so as to leave a flat lower surface of the wave guide 3|. The member 19 is spaced from the lower barretter socket '1| and has an axial length of approximately a quarter wave so as to form a quarterwave trap.

The hollow cylindrical quarter-wave trap 19 includes a ange 80 and a hollow cylindrical downwardly extending portion 3|, the length of which is substantially equal to a quarter wave, and the portion 8| is spaced from the terminal socket 1|.

The member 14 has a groove 14' formed in the outer surface thereof to form a spool for receiving a winding of resistance wire forming the compensating arm I2 of the bridge shown in Fig. 3.

The connector 12 includes a threaded ring 32 threaded into the inner surface of the member 14 and secured by the lock-nut 16, and three connection pins, 83, 34 and 85. The connection pin 93 is electrically connected to the threaded ring 92 by a conductor 96. The center pin 84 is connected to the barretter wire spring socket 1| by a conductor 81, and the pin 85 is connected to one end of the compensating resistor wire I2 by a conductor 6B, the other end of the wire I2 being connected to the metallic spool 14. It will be understood that insulated wire, such as enamel-covered wire, is utilized to form the resistor I2, and the surface of the groove 14 may be insulated by a suitable coating such as a coating of enamel, porcelain, or aluminum oxide to provide further safeguards against short-circuiting turns of the resistor I2.

It will be understood that a suitable connector (not shown) cooperating with the connector 12 is utilized for connecting the pins 83, B4 and 85 to corresponding conductors or terminals of the bridge shown in Fig. 3. Thus, the bridge terminal 83 is represented in Fig. 1 by the connection of the conductor B6 to the metallic housing 82 of the connector 12 and the other metallic parts of the wire holder are represented in Fig. 3 by a conductor 89. The pin 94 is connected to the bridge terminal 25 and the pin 85 is connected to the terminal 24 of the bridge shown in Fig. 3.

A direct current connection including the Wire I9 is thus formed from the pin 84 through the conductor 81, the socket terminal 1|, the ferrule G9, the wire I9, the second ferrule B9, the spring socket contact 61, the post 52, the head 58, the cap 58, the outer cylinder of the stub line 33, the wave guide 3|, the members 13 and 14, the connector ring 82, the connection 21, and the conductor 26 back to the pin 83. Likewise, a connection to the compensating resistance arm I2 is formed from the pin 85 through the conductor 88, the wire I2, the grounded end of the wire, the member 14, the connector ring 82, the conductor 86 and the pin 83. The compensating wire I2 is thermally connected to the metal surrounding the barretter wire I9, through the members 14, 15, 19, 3| and 33.

It will be observed that the lower spring socket contact 1| is supported centrally of the portion 3| by means of its flange 10, which in turn is clamped between the insulators 11 and I8 by the member 14 threaded into the member 13. The barretter wire unit I4 may be installed or replaced by opening the holder at either the upper or the lower end. For example, if the holder is to be opened the lower end, the lock-nut 16 and the member i4 are unscrewed; or if the holder is to be opened at the upper end, the cap 58 is unscrewed and the rod 52 is withdrawn to give access to the unit I4. Preferably, the spring pressure of the spring contact 61 is made greater than that of the spring contact 1| so that the unit I4 will be Withdrawn with the rod 52.

When the position of the wave trap member 3l? is adjusted by rotation of the knurled screw head 45, the internal screw remains ixed in angular position. The head 41 of the internal screw 4G limits leftward motion of the block 4| and the end of the hollow screw 44 limits motion of the block 4| to the right.

In the arrangement of Fig. 4 the supporting structure for the barretter unit I4 is made more compact by omitting the stub line 33 and instead providing a movable-probe adjusting mechanism 9| for tuning the line and matching impedance. As shown in Fig. 4, a rectangular hollow pipe wave guide 3| is provided, having lino-length adjusting mechanism 34', upper and lower barretter unit supporting members 92 and 93, and the probe adjusting mechanism Si.

The mechanism 34' includes the wave trap member 31 carried by a sliding block 4|, the screw 94 rigidly secured to the block 4|, an adjusting ring nut 95 and a lock nut 93. The member 31 is rigidly secured to the block 4| through a supporting post 91, and a ring nut retaining frame 98 is provided. The latter comprises a yoke-shaped block 99 (Fig. 6) secured in the end of the wave guide 3| in a suitable manner as by means of screws IDI and a slot closing stra ||l2 screwed to the ends of the bloei; 99 to form a nut retaining slot |03.

The barretter wire supporting members 92 and 93 are composed of a conducting material such as brass and are tted into upper and lower openings in the wave guide 3|', being rigidly secured thereto by soldering, brazing, or the like. The members 92 and 93 have openings for receiving the unit I4, and anged wave trap members |04 and |95 are tted into the openings so as to leave at upper and lower internal surfaces in the wave guide 3|. The members |94 and |05 are each a quarter wave in length, substantially, and are provided with su'cient clearance from the unit I4 and from the internal surfaces of the members 92 and 93 to form Wave traps, thereby avoiding any discontinuities in the wave guide 3| introduced by the presence of the opening for the barretter Wire unit I4.

For securing the unit I4 in the members 92 and 93, an upper spring clip or socket |05 is provided which is tted in the end of the member 92. A lower insulating socket member |01 is provided which is tted into the member 93. A threaded cap |08 is provided for securing the clip |06 in the member 92, and a positioning screw |99 may be adjustably mounted in the member |96. A member I I forming a lower cap and connector housing is threaded onto the member 93. To form a connector, an insulating bushing ||2 is mounted in the housing and a center pin ||3 is centrally secured in the bushing ||2. An insulating spacing cylinder ||4 is provided4 for enabling the insulator |01 to be secured in the member 93 by means of the insulator |I2 and the connector housing I I I.

The barretter unit I4 is provided with a downwardly extending terminal pin I|5, and a spring contacter ||6 adapted to engage the pin I|5 is secured to the top end ci the connector pin I I3.

As shown, the barretter wire unit I4 is of the Wollaston wire type having a silver-coated wire electrically connected between the lower ter'- minal pin and an upper terminal pin IIS, the center portion I I9 of the coated wire being etched away to leave a fine filament of platinum or other resistant material which forms the actual resistance of the unit and corresponds to the resistor I9 of Fig. 3.

The probe adjusting mechanism 9| comprises a pair of channeled members |2| and |22 adapted to t slidably over the upper and lower external surfaces of the wave guide 3|', a hollow post |23 tted into the channel block I2I, a hollow nut |24 threaded to engage the outer surface of the post |23, and a center post |25.

A top opening |26 is provided in the upper wall of the wave guide 3| of sufficient length to allow longitudinal adjustment of the probe mechanism. Clamping screws |21 are provided for adjustably securing the probe mechanism 9| in the desired position along the wave guide 3| (Fig. 5). The center post has a head |28 secured to the upper end of the hollow nut |24 and has a lower end |29 of reduced diameter to form a probe adapted to extend into the hollow wave guide 3| The nut |2I| is provided with a knurled head |3| at the upper end. The hollow post |23 has a reduced diameter opening tting the probe |29, and a large diameter opening providing ample clearance for the larger diameter portion of the post |25. Rotation of the hollow nut I2I| carrying the probe |29 serves for adjustment of the axial position of the probe |29, and the dimensions are such that the probe |29 may be moved a considerable distance into the wave guide 3|' or substantially withdrawn therefrom.

The variation in the position of the probe |29 serves to match the impedance of the line I3I to the resistance wire ||9 by varying in magnitude and phase the reflections from the probe |29 in such a manner as to cancel any reections from Wire IIS.

Since many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

l. In a microwave wattineter, in combination, a rectangular hollow wave guide adapted to receive microwave energy at one end and having an adjustable position closure at the other end, and a barretter mounting assembly intermediate the ends of said wave guide, said mounting assembly including a concentric adjustable tuning stub line laterally extending in one direction from the wave guide and a connector assembly laterally extending in the opposite direction from said wave guide with a barretter unit mounted between said stub line and the connector assembly, said stub line including a center conductor with a connection socket for the barretter unit in the end thereof and said connector assembly including a second connection socket for said barretter unit insulated from the wave guide.

2. Apparatus as in claim 1, in which a hollow cylindrical quarter-wave trap is provided surrounding the second connection socket for the barretter unit.

3. Apparatus as in claim 1, including a compensating resistor mounted in thermal connection with the wave guide for providing an ambient temperature compensation.

4. In a microwave wattmeter a hollow wave guide adapted to receive microwave energy, said guide having substantially parallel upper and lower walls, with opposed openings therein respectively laterally central thereof, a barretter wire unit mounted between said openings and athwart the wave guide, and members on either side of the wave guide for removably supporting said barretter wire unit including Wave trap means for preventing electrical discontinuity in the wave guide.

5. In combination, a hollow-pipe wave guide, a barretter wire mounted in the wave guide. and a temperature compensating resistor in thermal association with the wave guide, said barretter wire and said resistor being so connected in a bridge circuit that said resistor provides ambient temperature compensation for said barretter wire.

6. In combination, a hollow pipe wave guide having opposite walls with openings therein, a barretter wire unit mounted athwart the wave guide extending through said openings, and choke means for said openings arranged to prevent discontinuities in said wave guide.

7. Apparatus as in claim 6, wherein one of said choke means is a quarter-wave trap.

8. In a microwave wattmeter, in combination, a rectangular hollow wave guide adapted to receive microwave energy at one end and having a closure at the other end, and a barretter mounting assembly intermediate the ends of the wave guide, said mounting assembly including a concentric stub line laterally extending in one direction from the wave guide and a connector assembly laterally extending in the opposite direction from said wave guide with a barretter unit mounted between said stub line and the connector assembly, said stub line including a center conductor with a connection socket for the barretter unit in the end thereof and said connector assembly including a second connection socket for said barretter unit insulated from the wave guide.

9. In a microwave wattmeter a hollow wave guide adapted to receive microwave energy, said guide having substantially parallel upper and lower walls, with opposed openings therein respectively laterally central thereof, a barretter wire unit mounted between said openings and at the center thereof with a barretter wire unit mounted therein athwart the wave guide, and members on either side of the wave guide for removably supporting said barretter wire unit, at least one of said members including wave trap means for preventing electrical discontinuity in the wave guide.

10. Ultra-high-frequency apparatus for mounting a barretter element comprising a hollow wave guide short-circuited at one end with respect to ultra-high-frequency waves, a pair of members disposed in opposing walls of said guide each having a socket adapted to receive and to make contact with a barretter element to be mounted therebetween, one of said sockets being insulated from said guide with respect to unidirectional current, and one of said members including choke means for minimizing ultra-high-frequency Wave discontinuities in said guide.

11. Apparatus for mounting a barretter element or the like comprising a hollow Wave guide section having a pair of oppositely disposed Wall openings, a socket disposed opposite one opening adapted to conductively receive a barretter element or the like, said socket being conductively connected to said wave guide section, a second similar socket insulatingly mounted opposite the other opening, and a pair of tubular conductive members coaxially surrounding said second socket and connected together at one end, the innermost of said pair of tubular members being substantially a quarter wave length long at the normal operating frequency of said apparatus, whereby ultra-high-frequency continuity is maintained between said second socket and said wave guide, said second Socket and the outermost of said tubular members thereby providing output connection terminals for said barretter or like element.

12. Apparatus for mounting a barretter element or the like comprising a hollow wave guide section having a pair of oppositely disposed Wall openings, a socket disposed opposite one opening adapted to conductively receive a barretter 10 element or the like, said socket being conductively connected to said wave guide section, a second similar socket insulatingly mounted opposite the other opening, and a tubular member coaxially surrounding said second socket and connected at one end to said wave guide section adjacent said other opening, and a second tubular conductive member coaxial within said first tubular member and connected thereto at its end adjacent said other opening, the inner of said pair of tubular members being substantially a quarter wavelength long at the normal operating frequency of said apparatus, whereby ultra-highfrequency continuity is maintained between said second socket and said wave guide, said second socket and the outermost of said tubular members thereby providing output connection terminals for said barretter or like element.

HUGH E. WEBBER.

REFERENCES CITED The following referenlces are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,151,118 King Mar, 21, 1939 2,257,783 Bowen Oct. 7, 1941 2,402,663 Ohl June 25, 1946 2,407,068 Fiske Sept. 3, 1946 2,415,962 Okress Feb. 18, 1947 2,416,080 Bailey Feb. 18, 1947 2,434,508 Okress Jan. 13, 1948 Certificate of Correction Reissue No. 23,131 June 28, 1949 HUGH E. WEBBER It is hereby certified that errors appear in the printed specification 0f the above numbered patent requiring correction as follows:

Column 3, line 1U, for switch 28 read sur/'ich 29; line 18, for rcsistancos read reszstance; column 5, line 69, and column 6, line 17, for cap 58 read cap 5.9;

and that the said Letters Patent should be road with these corrections therein that the saine may conform to the record of the euse in the Patent Ofiice.

S1gned and sealed this 14th day of February, A. D. 1950.

THOMAS F. MURPHY,

Assistant 'ommz'ssz'oner of Patents. 

